1. Field of the Invention
The present invention relates to protective armor used on electrical cables and, more particularly, to armor used on electrical cables for use in subterranean wellbores.
2. Description of Related Art
Multiconductor electrical cables used to power wellbore equipment, such as electrical submergible pumping systems, must be capable of withstanding the high temperatures, high pressures and/or corrosive fluids often encountered within subterranean wellbores. As used herein, the term "high temperature" means temperatures of greater than about 180 F. and as high as about 500 F. The term "high pressure" means pressures as high as about 5,000 psi. Further, the term "corrosive fluids" means liquids and gases which can cause degradation to the cable's insulating materials and/or corrosion to the electrical conductors, such as liquids and/or gases containing hydrogen sulfide, carbon dioxide, brine, water, and the like.
Such electrical cables include an outer protective armor made from helically wrapped and interlocking metal material, such as galvanized steel. These cables should to be protected from damage since the submergible pumping systems will occasionally be pulled from the wellbores and reinstalled therein. During this retrieval and reinstallation significant damage can occur to the cable due to deterioration of the integrity of the metallic armor, such as by corrosion. In actuality, the use of metallic armor can accelerate corrosion of metallic bands and/or cable anchors used within the wellbore, as well as the wellbore tubing itself if the cable contacts the tubing. In many corrosive environments, special metal armor materials are used, such as stainless steel and Monel; however, these special metal materials add significantly to the cost of a cable. In addition, there are certain corrosive wellbore environments where these special metal materials will be damaged. There is a need for an armor material that can retain its integrity, to resist damage to the underlying cable, even after long term exposure to high temperatures, high pressures and corrosive fluids, and not cause other downhole components to corrode.
Another problem with existing cable is that the metallic armor adds significantly to the overall weight of the cable. Wellbore cable does not have the internal strength to uphold its own weight past about 50 feet. Therefore, wellbore cables are supported in some manner to the production tubing, such as by banding, clamps or cable anchors. If the weight of the cable could be reduced, then the number of the bands or cable anchors could be reduced by increasing the spacing between such bands or clamps. If the weight of the cable could be reduced, then the transportation costs can be reduced, especially when having to deliver large reels of cable to remote locations. There is a need for a wellbore cable with reduced weight over existing wellbore cables.